A poly-epoxy surface explored by Hartree-Fock ΔSCF simulations of C1s XPS spectra

Area of Science:

• Polymer Science
• Computational Chemistry
• Surface Science

Background:

• Poly-epoxy polymers are widely used but difficult to model due to structural disorder.
• Accurate characterization of polymer surfaces is crucial for understanding their properties and applications.
• X-ray photoelectron spectroscopy (XPS) is a powerful surface-sensitive technique, but spectral deconvolution can be challenging for disordered materials.

Purpose of the Study:

• To develop a combined theoretical and experimental approach for accurate modeling and analysis of poly-epoxy polymer surfaces.
• To improve the spectral resolution and chemical environment identification in XPS analysis of polymers.
• To demonstrate the utility of Hartree-Fock (HF) calculations, specifically the HF ΔSCF method, in interpreting XPS data.

Main Methods:

• Utilized well-characterized, defect-free poly-epoxy model samples for ultrahigh vacuum XPS experiments.
• Performed Hartree-Fock (HF) calculations using the ΔSCF method to determine C1s electron binding energies (BEs) and shifts (ΔBEs) for model molecules.
• Calculated relative binding energies using the HF ΔSCF method and relative intensities using the sudden approximation (SA).

Main Results:

• Achieved an excellent match between calculated and experimental XPS spectra.
• Identified nine distinct chemical environments under the C1s peak, significantly exceeding the three contributions typically resolved experimentally.
• Observed variations in binding energies due to second neighbor bound polarization, leading to localized and broader spectral contributions.

Conclusions:

• The combination of rigorous HF-ΔSCF theory and careful XPS measurements enables accurate assignment of polymer XPS spectra.
• HF-ΔSCF simulations substantially enhance the spectral resolution of XPS, offering a new method for polymer surface exploration.
• This integrated approach provides deeper insights into the complex chemical structures on polymer surfaces, overcoming limitations of purely experimental methods.